The present invention relates to an attachment for securing reinforcing plates, and a method for attaching such plates, in particular attachment to a spring-type vehicle brake actuator.
So-called “spring brake” actuators are employed to provide service, parking and emergency brake functions on vehicles such as commercial trucks, tractors and trailers equipped with lever-operated drum or disc brakes. Spring-type brake actuators are typically pneumatically operated, and are supplied with operating air from a compressed air source on the vehicle. These actuators also typically are arranged in a “fail-safe” manner, i.e., where the actuator defaults to a brake application state upon loss of operating air pressure. Such actuators may be employed on different types of brakes; FIG. 1 shows a conventional application of a pneumatic spring brake actuator 100 mounted at a mounting flange 103 via stud 101 and nut 102 to a disk brake caliper 200. Caliper 200 straddles brake disk 201 (shown in partial view) in the usual manner.
An example prior art spring brake actuator is shown in cross-section view in FIG. 1. Actuator housing 1 includes a rear cylinder 2 in which a rear piston 3 is displaceably arranged. The terms “front” and “rear” as used herein describe the directions facing toward and facing away, respectively, a vehicle brake to which the actuator is mounted. The inner wall of the rear cylinder and a chamber-side of the rear piston define a rear ventilation chamber 4. The other side of the rear piston bears on a brake actuator spring 5. This spring is also known in the art as a “power spring” or a “parking brake spring,” and these terms may be used interchangeably. For consistency herein, the terms “brake actuator spring” or “actuator spring” will be used.
The rear ventilation chamber is isolated from the spring side of piston 3 by an annular seal 6. An intermediate flange 8 (also known as a “wall”) separates rear cylinder 2 from a front cylinder 9. The intermediate flange 8 traversed by a seal 10 through which passes a sliding rod 11, formed as an extension of rear piston 3. The sliding rod 11 can be displaced in the intermediate flange 8 by the rear piston. A front ventilation chamber 7 within front cylinder 9 is delimited by the cylinder inner wall and a front piston 13 and annular diaphragm 14. The rear piston 3 and the front piston 13 are in non-coupled contact with one another by means of the sliding rod 11, such that the front piston 13 can be displaced in a brake application direction by the rear piston 3. An actuating rod 15 for actuating a brake lever of a vehicle brake is provided on the front side of the front piston 13.
When no pneumatic pressure is present in the FIG. 1 actuator unit, the brake actuation spring 5 applies a high spring force to rear piston 3, which in turn applies this force via sliding rod 11 to front piston 13 to cause the actuator rod 15 to apply the vehicle brake. In this state, the vehicle brake functions as a parking brake, preventing vehicle movement. When release of the parking brake is desired, the rear ventilation chamber 4 is filled with compressed air via port 19. As the force generated by the increasing air pressure on the front side of rear piston 3 exceeds the force generated by brake application spring 5, the rear piston 3 and sliding rod 11 move toward the rear of the rear cylinder 2, compressing spring 5. At the same time, as sliding rod 11 moves towards the rear, the force previously applied to front piston 13 is relieved, and a return spring 18 biases the front piston 13 toward the rear of front cylinder 9, thereby withdrawing actuating rod 15 away from and releasing the vehicle brake.
The foregoing type of spring brake actuator is complicated, difficult to produce and service, and suffer from a number of inherent problems. For example, in order to generate the very high brake application force needed to ensure full brake application in parking or emergency situations, the brake actuator spring must be powerful. As a result, brake actuator springs are large, heavy and store potentially dangerous amounts of energy when compressed. This requires that the spring brake housing to be heavily built, with relatively thick housing walls and high strength materials, to provide reliable containment of the spring and to provide an adequate foundation to absorb the reaction force of the spring as it presses against the rear end of the housing. This need is particularly acute in the case of prior art actuators, where the housing is continuously subjected to very high loads imposed by the actuator spring, and the housing must be designed to reliably withstand these loads during years of continuous exposure to harsh operating conditions. Ultimately, the need for such heavy housing construction undesirably increases the weight, size and cost of the actuator components. Another problem with prior art spring-type brake actuators is the potential for injury or property damage if the brake actuator spring is not properly handled during both actuator manufacture and servicing. The typical spring brake actuator is constructed with a rear portion being detachable from the front portion of the actuator. However, because this rear portion is often the sole component retaining the brake actuator spring, great care must be taken to ensure the spring remains captured or “caged” if the rear portion is to be removed, lest the spring or the rear portion of the actuator be accelerated in an uncontrolled manner away from the housing as it is being disassembled for service. Similar concerns exist during manufacture, where the springs must be carefully controlled during actuator assembly to prevent their inadvertent escape.
In view of the problems with these type of prior art spring-type brake actuators, an improved actuator has been developed which is safer, lighter, simpler, more reliable, less costly and/or safer to assemble and service. This spring brake actuator, the subject of U.S. patent application Ser. No. 11/012,313 (the disclosure of which is incorporated herein by reference in its totality), eliminates the need for heavy housing structures and extra brake actuator spring capture features by substantially rearranging the primary components of a spring brake actuator. As shown in FIG. 2, in one embodiment the brake actuator spring 300 is relocated to the front portion 301 of the actuator housing, occupying a region 302 between the front service brake actuator 303 and the rear parking brake release actuator 304. When the spring brake actuator is inactive (i.e., no pressure exists in either the front or rear chambers), the brake actuator spring applies the vehicle brake by pressing on the service brake actuator 303 via an intermediate spring plate 305, and the service brake actuator in turn presses the brake actuator rod 306 forward in a brake application direction. The parking brake release actuator 304 remains in the rear chamber 307 of the actuator housing, but instead of pressing directly on the service brake actuator (as in the previous prior art example), its attached shaft 308 is now solidly affixed to the rear side of the intermediate spring plate 305. Thus, when air pressure is applied to the rear chamber, rather than compressing the brake actuator spring into the rear end of the actuator housing, as in the prior art, the present invention's parking brake release actuator draws the intermediate spring plate toward the intermediate body portion of the actuator 309 (hereinafter, the “housing intermediate flange”), compressing the brake actuator spring against the front side (or “floor”) of the intermediate flange to remove the spring's force from the actuator rod. For servicing and other purposes, the parking brake may also be manually released, as shaft 308 is provided with a threaded bolt 310 extending through aperture 311 and threaded member 312. The threaded bolt 310 may be engaged with member 312 to withdraw the service brake actuator toward the housing intermediate flange 309 to positively compress and hold spring 300 therein. This new spring brake actuator arrangement preserves the “fail-safe” nature of prior art spring-type brake actuators (i.e., loss of pressure in the rear chamber results in the brake actuator spring re-applying the brake), while also positively capturing the spring between the spring plate and the intermediate flange. Among the many advantages resulting from the rearrangement of the previously known actuator components in this new spring brake actuator design is a significant decrease in the structural requirements on the housing (in particular, the rear portion of the housing), and the inherent self-capture of the powerful brake actuator spring, which makes actuator manufacture and servicing inherently safer.
A disadvantage of prior spring brake actuators is top portion of the rear chamber typically does not possess a great deal of inherent strength against being pulled inward (i.e., toward the service brake actuator) due to the relatively thin section of the rear chamber cover near its center. This can becomes a particular problem when the rear chamber cover is used to provide a base for drawing the service brake actuator outward in order to compress the power spring, either because the cover is too thin to form a sufficient number of threads for a threaded rod to engage without thread shearing, or in the case of a withdrawal rod which rests against an outside surface of the rear chamber, the chamber end is too thin to prevent chamber collapse as the power spring is compressed.
Accordingly, it is an object of the present invention to provide a rear chamber reinforcement and a unique method of attaching the reinforcement which does not rely on welding, gluing, bolted connections or other conventional attachment approaches to secure the reinforcements.
It is a further objective of the present to provide a reinforcement and a method of attaching the reinforcement which can be executed quickly, easily, reliably and at low cost.
It is another objective of the present invention to provide a reinforcement and a method of attaching the reinforcement which provides an enhanced environmental seal seating surface in a simple and cost-effective manner.
These and other objectives are met by a unique combination of reinforcement plates and a reinforcing plate crimping method, in which reinforcing plates with progressively smaller internal apertures are stacked about a center aperture of a rear chamber cover, and the innermost plate is deformed about is inner radius (for example, by crimping) laterally outward into the interior of the rear chamber. This deformation simultaneously draws the reinforcing plates into firm contact with the outside surface of the rear chamber cover, while also capturing the rear chamber cover therebetween. In a preferred embodiment, as the innermost reinforcing plate is crimped into place, a concentric ridge is formed in the portion of the rear chamber cover around the reinforced hole, thereby forming a dust-cover-retaining lip surface during the single reinforcement crimping operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.